This invention relates to a circuit breaker, and more particularly, to a circuit breaker which prevents the circuit breaker operating handle from being positioned in an OFF position if the operating contacts of the circuit breaker are not separated.
In general the function of a circuit breaker is to electrically engage and disengage a selected circuit from an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.
There are two modes by which the operating mechanism for the circuit breaker can disengage the operating contacts: the circuit breaker operating handle can be used to activate the operating mechanism; or a tripping mechanism, responsive to unacceptable levels of current carried by the circuit breaker, can be used to activate the operating mechanism. For many circuit breakers, the operating handle is coupled to the operating mechanism such that when the tripping mechanism activates the operating mechanism to separate the contacts, the operating handle moves to a FAULT position.
To engage the operating contacts of the circuit breaker, the circuit breaker operating handle is used to activate the operating mechanism such that the movable contact(s) engage the stationary contact(s).
The present invention is directed to the rare occasion when one or more pairs of operating contacts become inseparable during operation. In a typical circuit breaker, it is possible that when the operating contacts become inseparable, the operating handle of the circuit breaker can be moved to the OFF position even though the operating contacts are not separated. When the operating contacts become inseparable, it is also possible that the level of current flowing through the circuit breaker may cause the tripping mechanism to activate the operating mechanism such that the operating handle can be moved to the OFF position without separating the operating contacts. Accordingly, even though the contacts are engaged and carrying current, the operating handle can be locked in the OFF position to indicate that the circuit breaker is OFF.
U.S. Pat. No. 4,829,147 (Schiefen et al.) relates to a circuit breaker that positively indicates the position of the circuit breaker contacts. In the apparatus of U.S. Pat. No. 4,829,147, when the contacts are locked and an operator attempts to move the operating handle to the OFF position, a shuttle pivoted on the circuit breaker operating mechanism rotates to block the movement of the handle to the OFF position.